Drive for seismographic record strips



Dec. 5, 1950 R. L. HENSON, JR, EI'AL 2,532,911

DRIVE FOR SEISMOGRAPHIC RECORD STRIPS Filed Dec. 3, 1947 INVENTORS JOHN M/LL/NGTON 8 ROBERT L. HE/VSOMJR ATTOR EYS Patented Dec. 5, 1950 DRIVE FOR SEISMOGRAPHIC RECORD STRIPS and John W. Millington,

Robert L. Henson, Jr.,

Beaumont, Tex.,

assignors to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey Application December 3, 194. Serial No. 789,426

2 Claims. 1

This invention relates to a drive for seismographic record strips for the attainment of uniform motion of the record strip, usually a photographically sensitive paper, in a seismograph the present invention the desired result is achieved through the use of a vibrating reed inverter feeding into a synchronous motor, the inverter being powered from a battery and being synchronized with a standard frequency generated under the control of a tuning fork or equivalent device.

The objects of the present invention relate to securin proper uniform feed of a sensitized record'strip in simple and reliable fashion and will be apparent from consideraton of the following description read in conjunction with the accompanying drawing in which the figure illustrates in the form of an electrical and mechanical diagram the port ons of the apparatus constituting a preferred embodiment of the invention.

A tuning fork indicated at 2 constitutes the master osci lation control and is associated with a conventional driving system including a pickup coil 4 coupled through a transformer 6 to a vacuum tube amplifier 8 which, through a transformer I0, provides a feed-back to the fork driving coil l2. The operation of this drive is conventional, the core of the pck-up coil 4 being in the form of a permanent magnet, the reluctance of the magnetic circuit of which is changed through the vibration of one of the arms of the tuning fork. The amplified signals thus produce feed-back through the driving coil and maintain the tuning fork in oscillation. A tuning fork of any desired frequency may be used but commonly in this work a 100 cycle per second frequency is used since intervals may then be conveniently timed in terms of decimal parts of a second.

A condenser. l4 transmits output signals from the tube 8 to an amplifier tube I which, through a transformer It, drives a push-pull power amplifier stage comprising the tubes 20 and 22. The output from this last amplifier is fed to the primary of a transformer 24 having a pair of secondary windings. One of these secondary windings indicated at 26 drives a small synchronous motor forming part of a timing device 28 arranged to chop a beam of light so as to project timing markings through a lens system indicated at 30 upon the sensitized record strip, for example, of paper indicated at 32. This arrangement is conventional and through it timing markings generally in the form of transverse lines are projected on the record strip every hundredth of a second. It will be evident, however, that unless the speed of the record strip 32 is uniform these markings would not be uniformly spaced on the strip. The invention is primarily concerned with the securing of uniform motion of the strip.

The strip 32 is fed from a supply reel 34, being wound up upon a take-up reel 36, the feed being accomplished by means of a roller 38 driven by a synchronous motor 44, the paper strip being pressed against the roller 38 by means of pressure rollers 40 and 42. This camera arrangement is also convent'onal, the light beams from the oscillograph elements being projected on the sensitized paper where it passes over the roller 38. The details of the camera arrangement need not be indicated in view of their conventional aspects.

The inverter provid ng alternating current to the motor 44 comprises a vibrating reed 46 arranged to be driven by the electromagnet 48 and provided with conventional contacts for producing reversal of current in the output lines upon vibration of the reed. A battery 50 having a voltage, for example, of 6 volts supplies the current to the inverter under the control of the switch 52. The arrangement of transformer 56 and the condensers indicated at 58 provides an inverter output which is approximately sinusoidal and proper for the drive of the synchronous motor 44.

A vibrating reed inverter of the type so far described will normally maintain a generally constant frequency output and in the present case, still assuming a frequency of cycles per second, the vibrating reed would be adjusted so that in free operation it would normally produce an output substantially constant at 100 cycles. In accordance with the present invention substantially absolute constancy of frequency is insured by feeding through a second transformer sec- 1w qu ncy of operation of the tuning fork. In any ondary It a synchronizing signal through the reed driving coil 48. The synchronizing signal which is thus fed may be very small, for example, only about one watt at one volt. This small signal will correct any tendency of the reed to depart from precise 100 cycle operation and the sole error in frequency which might be involved be that due to the minute changes in freevent, it will be evident that the system enforces precise uniform spacing of the timing marks which are made by the timing device 28 on the sensitized strip.

It may be questioned why the power output derived from further amplification of the tuning fork signals should not be used directl to drive the motor 44. This, however. is not feasible for field work since the motor It requires substantial power for its operation, remembering that the record strip must travel at a quite high rate of speed, and the amplifying system which would be required would have a very low efficiency as compared with the vibrating reed system which can provide a quite substantial power output at high efficiency and may be maintained in precise synchronism with the tuning fork with very little expenditure of sychronizing power. It may also be noted that the tuning fork and the timing device it may be started running before recording by the camera it is started. This permits starting transients to die out in the tuning fork and the driving motor to insure accurate spacing of the timing lines- The camera motor is, of course, started by closing the switch If in the direct current input line to the inverter. The inverter accordingly runs only when the motor is to be operated, saving power which is at a premium in the seismograph instrument truck used in field work.

The B power for the amplifying system may be derived in usual fashion using a vibrator or dynamotor driven by the storage battery 80.

What we claim and desire to protect by Letters Patent is: v

1. In combination, means for advancing a record strip, a synchronous motor for driving said advancing means, a vibrating reed inverter for supplying alternating current for driving said synchronous motor, said inverter including an electromagnetic driving device for its reed and contact means engageable by said reed. a low voltage current supply. connections between the low voltage current supply, said driving device and said contact means through which said current-supply would drive said reed at an approximately constant frequency, a tuning fork, driving means for the tuning fork, an amplifier supplying alterating current at relatively low power at the tuning fork frequency, means supplying said alternating current to said connections to maintain vibrations of said reed at the tuning fork frequency, thereby to control the frequency of the alternating current supplied by said inverter, and a synchronous motor for driving a timing device adapted to space timing markings on said record strip, said last mentioned synchronous motor being connected to said amplifier and enforcing precise uniform spacing of said timing markings.

2. In combination, means for advancing a record strip, a synchronous motor for driving said advancing means, a vibrating reed inverter for supplying alternating current for driving said synchronous motor, said inverter including an electromagnetic driving device for its reed and contact means engageable by said reed, a low voltage current supply, connections between the low voltage current supply, said driving device and said contact means through which said current supply would drive said reed at an approximately constant frequency, means supplying an alternating current at fixed frequency and at relatively low power to said connections to maintain vibrations of said reed at said fixed frequency, thereby to control the frequency of the alternating current supplied by said inverter, and a synchronous motor for driving a timing device adapted to space timing markings on said record I strip, said last mentioned synchronous motor being connected to said fixed frequency alternating current supply and enforcing precise uniform spacing of said timing markings.

ROBERT L. HENSON, JR. JOHN W. MILLINGTON.

REFERENCES crran The following references are of record in the file of this patent:

UNITED STATES PATENTS 

